1. Field of the Invention
The present invention relates to a hydraulic sealing device including a sealing ring which is mounted in an annular sealing ring groove defined in an outer periphery of a shaft member, so that it is brought into pressure contact with both a sealing inner-peripheral surface of a housing relatively rotatably fitted over the outer periphery of the shaft member and one of the sealing sides of the sealing ring groove.
2. Description of the Prior Art
Such a hydraulic sealing device is already known, as disclosed, for example, in Japanese Patent Application Laid-open No. 262171/92.
When the shaft member is made of an aluminum alloy which is easily worn, there is a problem that the sealing sides of the sealing ring groove abutting against the sealing ring are worn quickly, and this wearing is considerably increased if a hard foreign matter such as an iron powder is contained in the working oil. Therefore, if a small amount of the oil is leaked from an abutment of the sealing ring for washing away the foreign matter along with such leaked oil, the foreign matter can not easily be caught between the sealing ring and the sealing sides of the sealing ring groove and hence, it is possible to effectively avoid the wearing.
A hydraulic sealing device is also known from Japanese Utility Model Application Laid-open No. 41153/92, in which the shape of an abutment of a sealing ring is of a so-called triple-stitch type having overlapped portions axially and radially. In this sealing ring, the abutment is always locked, leading to an enhanced sealability, as compared with a sealing ring having an abutment of a straight shape.
However, in the shape of the abutment of the sealing ring described in Japanese Patent Application Laid-open No. 262171/92, there is a problem that the sectional area of a flow path in the abutment is varied substantially due to the thermal expansion of the sealing ring attendant to a change in temperature and as a result, it is difficult to stably leak a given amount of the oil. In addition, if a sealing ring having the shape of the abutment described in Japanese Utility Model Application Laid-open No. 41153/92 is to be produced by an injection molding process, an arm circumferentially protruding from the abutment is stuck to and pulled by a stationary die, whereby the arm is deformed. When the sealing ring having the deformed arm is mounted in the sealing ring groove and used, there is a possibility that the amount of oil leaked is unstable, and the foreign matter intrudes into between the arm and the sealing ring, thereby causing an abnormal wearing.